Field of the Invention
The present invention relates to an organic light emitting display device.
Discussion of the Related Art
A touch screen has been used, which may allow a user to directly input information on a screen by using a finger or pen instead of a mouse or keyboard, which has been used as an input device of a flat panel display device, or a key pad used as an input device of portable electronic equipment. The touch screen has an advantage in that anyone may easily manipulate it, and thus its application has been increased.
With the development of information society, various demands for display devices for displaying picture images have been increased. In this respect, various display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting display (OLED) device have been recently used.
The organic light emitting display device of the various display devices may be driven at a low voltage, and is characterized in a thin profile, an excellent viewing angle, and a fast response speed. The organic light emitting display device includes data lines, scan lines, a display panel having a plurality of pixels formed at crossing portions between the data lines and the scan lines, a scan driver supplying scan signals to the scan lines, and a data driver supplying data voltages to the data lines. Each of the pixels includes an organic light emitting diode, a driving transistor controlling the amount of a current supplied to the organic light emitting diode in accordance with a voltage of a gate electrode, and a scan transistor supplying the data voltages of the data lines to the gate electrode of the driving transistor in response to the scan signals of the scan lines.
A threshold voltage and mobility of the driving transistor may be varied per pixel due to process deviation during manufacture of the organic light emitting display device or a threshold voltage shift of the driving transistor, which is caused by long time driving. If the same data voltage is applied to the pixels, the same current Ids of the driving transistor should be supplied to the organic light emitting diode. However, even though the same data voltage is applied to the pixels, the current Ids of the driving transistor, which is supplied to the organic light emitting diode, is varied per pixel due to a difference in a threshold voltage and mobility of the driving transistor between the respective pixels. As a result, even though the same data voltage is applied to the pixels, a problem occurs in that luminance emitted by the organic light emitting diode is varied per pixel. To solve the problem, a method for compensating for a threshold voltage and mobility of a driving transistor has been suggested.
The method is categorized into an internal compensation method and an external compensation method. The internal compensation method refers to compensate for the threshold voltage of the driving transistor by sensing the threshold voltage within the pixel. In more detail, the internal compensation method supplies a predetermined data voltage to the pixel, senses the current Ids of the driving transistor of the pixel through a predetermined sensing line in accordance with the predetermined data voltage, converts the sensed current to digital data, and compensate for digital video data, which will be supplied to the pixel, by using the sensed digital data.
If the organic light emitting display device compensates for a threshold voltage and mobility of a driving transistor of each of pixels in accordance with the external compensation method, the organic light emitting display device includes sensing units for sensing a current Ids of the driving transistor of each of the pixels by converting the current Ids to digital data. However, even though the same current Ids of the driving transistor is sensed by the sensing units, a problem occurs in that a difference between sensing data output from the sensing units is generated due to a difference in sensing capability between the sensing units. For this reason, a problem occurs in that sensing accuracy is lowered.